Demineralization of the tooth surface
caused by bacteria
Chemicoparasitic theory (1890)
● Proposed in 1890 by W. D. Miller in his book "The
microorganisms of the human mouth" based upon the work
done in Robert Koch’s laboratory in Berlin
● Acid and parasite
● Showed that the degradation of carbohydrate-containing foods
resulted in acid formation and was able to demonstrate this
process in vitro with isolated oral bacteria and extracted teeth.
● Concluded that dental caries was caused by multiple species of
● No specific bacteria was implicated – “non-specific”
● Dental caries was caused by multiple or all species of
oral bacteria “Non-specific plaque hypothesis„
● Proper prevention is therefore is to remove or
minimize multiple bacterial species.
Practice of tooth brushing, flossing and professional
The specific plaque hypothesis and
● In 1924, Clark isolated streptococci from human
carious lesions, and named Streptococcus mutans
● In 1960, Keyes showed that ‘caries-free’ hamsters
develop dental caries only when caged together with
‘caries-active’ hamsters - Infectious and
● The bacteria previously referred to as S. mutans are
actually seven distinct species now called mutans
● MS are the principal etiological agents of dental caries
Microbial etiology of dental
Mutans Streptococci (MS)
Requires a relatively high proportion (2-10%) of mutans
streptococci within dental plaque.
Possess adherence activity (to tooth surface)
Produce higher amounts of acid from sugars than other bacterial
types, and possess acid tolerance
Produce extracellular polysaccharides from sucrose.
Dentin, root caries, acidogenic, acid tolerant
● Actinomyces viscosus
Acidogenic and acid tolerant
Current diagnosis and
● Future diagnostics using microbiology
Detection and monitoring of cariogenic bacteria others
● Potential preventive measures based on
Preventing bacteria from colonizing tooth surface
Local and topical antimicrobial agents
Early acquisition and
● Mutans streptococci appear in the mouth after teeth
have erupted as they need solid surfaces to colonize.
● The establishment of the bacteria seems rather slow
the first two years, and one talks about a "window of
infectivity" which would open after about two years.
● There seems to be a family pattern as similar types of
bacteria have been found in the mouth of child and
parents, in particular mothers.
Mutans Streptococci -
● Global distribution – found in all populations
● High counts - 106/ml saliva
● Usually, serotype c (Streptococcus mutans) is
the dominating serotype. One person can
have several serotypes (both Streptococcus
mutans and Streptococcus sobrinus).
Dental caries in relation to mutans
● Gram-positive bacteria which are commonly isolated from the
● Cariogenic, highly acidogenic organisms, however, has low
affinity for tooth surfaces.
● Associated more with carious dentine and the advancing front of
caries lesions rather than with the initiation of the disease.
● Usually lactobacilli comprise less than 1% of the total cultivable
microflora. However, their proportions and prevalence may
increase at advanced caries lesions both of the enamel and of
the root surface.
Sugar metabolism of
● Acid production (lactate) from glucose and fructose
● Formation of extracellular polysaccharides (glucose polymer,
fructose polymer) from the energy of the disaccharide bond of
sucrose. (glucosyltransferase, fructosyltransferase)
- Increase the thickness of plaque substantially
- Changing the chemical nature of its extracellular space from
liquid to gel.
- The gel limits movement of some ions, protects the plaque
biofilm from salivary buffering. Plaque which has not had
contact with sucrose is both thinner and better buffered.
The metabolism of S.
● Key to the pathogenesis of dental caries
- The fermentation of these carbohydrates is the principal
source of energy for S. mutans
Genome sequence shows that S. mutans can metabolize a
variety of carbohydrates than any other G(+) microorganism
- The glycolytic pathway leads to the production of
to lactic acid (by LDH activity), formate, ethanol and
- The acidic environments are responsible for the damage
- Acid tolerant – based on a membrane-bound, acid stable,
Virulence factors of S.
● Production of acid
Wall-associated protein A (WapA)
S. mutans LraI operon (SloC)
Glucan-binding proteins A and C
Two methods of attachment
● Sucrose independent –using ionic and lectin like interaction
- Adhere to salivary agglutinin glycoprotein (SpaP:
Streptococcal protein antigen P, aka antigen I/II)
- Isogenic mutants of SpaP
- Passive immunization study
- Adhere to other bacteria, the extracellular matrix and
epithelial cell-surface receptors
Two methods of attachment
● Sucrose dependent
- Adhere to tooth surface by synthesizing glucans by
- Glucan promotes cell-cell aggregation by interacting with
surface-associated glucan binding protein
Virulence factors of S.
Ecological basis of dental
● Environmental changes
A variety of environmental signals in complex communities
● Ecological shift
The signal triggers adaptation to acid environment
● Biofilm characteristics
Virulence properties of S.
● Adhesion, acidogenicity, and acid tolerance
● Each of these properties works coordinately to alter dental plaque
● The ecological changes are characterized by increased
proportions of S. mutans and other species that are similar
lacidogenic and aciduric.
● The selection for a cariogenic flora increases the magnitude of
the drop in pH following the fermentation of available
carbohydrate and increases the probability of enamel
Novel approach to dental
caries Replacement therapy
● Replacing a specific bacterial pathogen with a non-
pathogenic strain, an effector strain
- should not cause disease itself or disrupt the ecosystem
- must persistently colonize the host tissue at risk and
prevent colonization or outgrowth of the pathogen
- should possess a high degree of genetic stability
● Possible life-long cavity protection
● Little or no risk of side effects
● Minimal patient education and compliance
Replacement therapy for the
● Lactate dehydrogenase (LDH)-deficient mutants
Streptococcus rattus LDH mutants were shown to have little or no
cariogenic potential in vitro and in various rodent models.
● Lantibiotic production
S. mutans strain (JH1000) produces a lantibiotic called mutacin
1140 capable of killing virtually all other strains of mutans
streptococci against which it was tested.